ÇBAG kullanılan rüzgar türbinlerinin güç kontrol döngüsüne hassasiyet ve sağlamlık analizi uygulanması

In this paper, the stator power equations are utilised to derive the plant model of the power loop and its controller; and the enhancement of the power loop control of doubly-fed induction generator (DFIG) based wind turbines is accomplished. The main electrical components of a typical DFIG based wind turbine, which are back to back bidirectional partly rated converters, a DC-link capacitor placed between these converters, and protection devices of power electronic components, e.g. a rotor crowbar or/and a DC-link brake chopper, are depicted. DFIGs can provide maximum power extraction and are suitable for variable speed operation (the speed range is ± 33% around the synchronous speed). The converter topology used in this study is a threephase voltage source converter (VSC) consisting of insulated gate bipolar transistors (IGBTs) controlled by a pulse width modulation (PWM) switching technique. The traditional control approach for the power loop of the DFIG wind turbine systems is to use PI control. However due to the nature of the plant model considered in this research, using a PI controller for the power loop yields a first order transfer function that allows setting only the bandwidth, but unfortunately not the damping. Therefore, to be able to set the damping as well, the PI controller is replaced with a PID controller. However, the tuning process of the PID controller is more complicated than that of the PI controller, and selecting the derivative time constant, proportional and integral gains needs to be done very carefully. The relevant transfer functions of the power loop are extracted. The sensitivity analysis is applied to these transfer functions where the current loop of the rotor side converter (RSC) and both the current and voltage loops of the grid side converter (GSC) control are tuned for the fixed values of the natural undamped frequency (ωn in rad/s or fn in Hz) and the damping ratio (ζ). In the control sensitivity analysis, each time one of the power loop PID tuning parameters is varied while other two parameters stay fixed at their predefined values. The values of damping ratio, natural undamped frequency and KD (derivative time constant) are selected as 0.7, 0.8, 0.9, 1, 1.1; 1Hz, 1.5Hz, 2Hz, 2.5Hz and 0.1s, 0.2s, 0.3s, 0.4s, respectively. The first step of the sensitivity analysis is to vary the natural undamped frequency from 1Hz to 2.5Hz in case of fixed damping ratio (ζ) and KD. Secondly, the damping ratio is varied between 0.7 and 1.1 while keeping the natural undamped frequency and KD. Finally, the KD is varied from 0.1s to 0.4s for the fixed values of natural undamped frequency and damping ratio. Thus, the reasonable search space for tuning parameters and gains for the PID controller used as the power loop controller is investigated. In doing so, the ‘best’ operating points of the tuning parameters for the power control considered in this research are determined. Based on the 'best' operating points of the tuning parameters, the robustness analysis is then conducted by applying ± 20% change to the stator voltage and ± 10% change to the stator selfinductance and mutual inductance. Thus, the control system design is validated to be robust under the physical changes of the stator voltage, stator selfinductance, and the mutual inductance. The work done in this paper is consistent with the simulation results obtained by PSCAD.